where \(0 \le \zeta _k \le 1, k = 1, ... ,K\) , is the energy harvesting efficiency at \(SU_k\) , and \(P_t\)  is the transmission power of the PT. We consider all energy harvesting coefficients of SUs are the same, \(\zeta _1 = \zeta _2 = ... = \zeta _K = \zeta \) . It is worth mentioning that in this paper, we consider non-intended limited energy harvesting from the primary transmitter, which is enough for low-power sensor networks [1]}, [2]}. Hence, in the multi-hop scenario, the transmit power of each \(SU_k\)  is limited, and we assume the transmission range is one hop. Therefore, we only consider the primary signal as the source of energy harvesting, as expressed in (REF )[2]}.
